In applicant's Canadian Patent Application No. 2,354,903 and corresponding U.S. patent application Ser. No. 10/039,571 published under No. US 2003/0031415 A1 and incorporated herein by reference, there is disclosed a polarization combining fused-fiber optical coupler which is operational in a broad wavelength bandwidth, i.e. as a broadband coupler. It is made of two polarization maintaining (PM) fibers spliced to two standard single mode (SM) fibers which extend and are fused and drawn to make a coupling zone. In this arrangement, the linearly polarized light is injected into the PM fibers and oriented so that the polarization in one of the PM fibers is orthogonal to that of the other PM fiber, and when this light passes through the input arms of the SM fibers (the axes of which are aligned with the birefringent axes of the PM fibers) and into the coupling zone, the two polarizations are combined in this zone and emerge from one output fiber of the coupler with only a minimal power transmission going to the second output fiber.
Furthermore, a polarization selective phase shifting, splitting and combining optical device based on a Mach-Zehnder structure is disclosed in applicant's Canadian Patent Application No. 2,357,991 and corresponding U.S. patent application Ser. No. 10/090,128 published under No. US 2003/0063834 A1. In this MZ structure, a relatively small phase shift is produced, typically of one π, by splicing in one of the arms of the central zone a segment of a PM fiber. A broadband polarization splitter or combiner may thus be achieved with a Mach-Zehnder structure where in the central zone, between the two couplers, a segment of a PM fiber is spliced in one of the arms to provide the required phase shifting. This is also described, for instance, in applicant's Canadian Patent Application No. 2,357,955 and corresponding U.S. patent application Ser. No. 10/045,190 published under No. US 2003/0063833 A1 with reference to FIG. 3 embodiment. This prior patent application also makes reference to broadband WDM fused fiber couplers.
Another all-fiber depolarizer with a polarization combiner based on a Mach-Zehnder interferometer structure is disclosed in applicant's Canadian Patent Application No. 2,393,172 and corresponding U.S. patent application Ser. No. 10/397,672 which also mentions a PPC used in order to scramble pump polarization. When it is desired to achieve a broadband operation with the PPC, inverted WICs (wavelength independent couplers) are utilized therewith.